Method of preparing photographic emulsions



Patented Oct. 21, 1952 METHOD OF PREPARING PHOTOGRAPHIC EMULSIONS Henry C. Yutzy and Frederick J. RusseH, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application August 13, 1947, Serial No. 768,476

13 Claims. 1

This invention relates to a method for prep-aring washed silver-halide photographic emulsions in which the silver halide is preparedin a solution of gelatin, mixed with gelatin derivative, acidcoagulated, washed, and then re-dispersed.

Heretofore in the making of photographic emulsions gelatin has been principally depended upon as the carrier for the silver halide and as the peptizing agent employedin its preparation. In these normal methods of preparing silverhalide emulsions the emulsion maker has in the past been limited in the scope of his operations bythe physical properties peculiar to gelatin.

These characteristics have necessitated limitations on the concentration of silver halide and of gelatin in photographic emulsion formulae to values which are not most desirable for all purposes. For instance, emulsions of high concentration of silver halide have been diflicult to prepare. Limitations have been imposed on the emulsion maker regarding the conditions of dilution during emulsion making since emulsions with too high water content are difiicult andundesirable to coat. In addition, the technician has been obliged to limit the minimum concentration of gelatin in the washing operation in which soluble salts are removed. It has been the usual practice heretofore in preparing washed emulsions to set the dispersion of silver halide in gelatin to a jelly, noodle thi jelly and wash by osmosis with cold water preferably with a hardener added thereto. Under such conditions a minimum gelatin concentration of approximately 3-4% is permissible, and this limitation has hampered the free operations of the emulsion maker in preparing emulsions of this type.

One object of our invention is to provide a method of preparing photographic emulsions of the washed type in which the difliculties previously met with are absent. Another object of our invention is to provide a method of washing silver-halide dispersions in which substantially all of the liquid may be removed therefrom in the course of the washing operation. A further object of our invention is to provide a method of preparing silver-halide dispersions using gelatin derivatives in their preparation. Other objects of our invention will appear herein.

We have found a ready means of avoiding the limitations which have heretofore been met with in the preparation of photographic emulsions. Our methodis especially valuable in expanding the possible conditions for the manufacture of photographic silver-halide emulsions of diiferent speeds, contrasts, and other photographic characteristics. In addition, the method in accordance with our invention offers a simple means to prepare emulsions of high silver concentration which is especially valuable in the manufacture of films bearing large quantities of silver per unit area.- In its broadest aspects, our invention involves the mixing of gelatin derivatives into dispersions of silver halide in gelatin in sufficient amount to impart coagulating properties to the entire mass. The gelatin derivatives which are employed in accordance with our-invention may bepreparedlfrom gelatin by adjusting: a solution or suspension of gelatin to a pH value of 8 to 11 or more with a suitable base, such as sodium hydroxide or ammonium hydroxide and then adding a reagent which will react therewith, ordinarily at a temperature of 25-60 C. The reaction between the reagent and the gelatin usually takes 5-20minutes after which the gelatin derivative may be employed either in the solution in which it is formedor in solid condition. The gelatin derivatives which have been found to be especially useful in the process in accordance with our invention are those of the aromatic sulfonyl chlorides, the carboxylic acid chlorides, the carboxylic' acid anhydrides, especially of the dicarboxylic type, the aryl isocyanates, and the IA-diketones. The following" compounds have been found to be useful for preparing gelatin derivatives suitable for use in our invention:

Sulfonyl chlorides Benzene sulfonyl chloride p-Methoxybenzene sulfonyl chloride p-Phenoxybenzene sulfonyl chloride p-Bromobenzene sulfonyl chloride p-Toluene sulfonyl chloride m-Nitrobenzene sulfonyl chloride m-Sulfobenzoyl dichloride Naphthalene-beta-sulfonyl chloride p-Chlorobenzene sulfonyl chloride 3-nitro-4-aminobenzene sulfonyl chloride m-Carboxy-4-bromobenzene sulfonylchloride 1 chlorosulfonyl 2 hydroxy-3-naphthoic acid quinoline-8-sul fonyl chloride m-Carboxybenzene sulfonyl chloride 2-amino-S-methylbenzene-sulfonyl chloride Carbomylic acid chlorides Phthalyl chloride p-Nitrobenzoyl chloride Benzoyl chloride Ethyl chlorocarbonate Furoyl chloride entire mass.

3 Acid anhydrides Phthalic anhydride Benzoic anhydride Succinic anhydride Maleic anhydride Isatoic anhydride Isocyanates Phenyl isocyanate p-Bromophenyl isocyanate p-Chlorophenyl isocyanate p-Tolyl isocyanate p-Nitrophenyl isocyanate Alpha-naphthyl isocyanate Beta-naphthyl isocyanate 1,4-diketcmes Acetonyl acetone Dimethyl acetonyl acetone In its broadest aspects our invention comprises the formation of the silver-halide grains in an aqueous solution of gelatin whereby good dispersion is obtained followed by the addition to this solution of a gelatin derivative in sufficient proportion to impart coagulating properties to the The amount of gelatinderivative which must be added to insure satisfactory coagulation is determined by two features: (1) the concentration of normal gelatin which ..is present and (2) the concentration of salt which is present in the solution. In the case of emulsions which contain alkali metal nitrate equivalent to the silver halide formed in the double decomposition reaction, the ratio of gelatin derivative to normal gelatin should be of the order of 4 to 1. If large quantities of salt are present, the ratio of the gelatin derivative to the gelatin may be as little as 2 to 1 for good emulsion coagulation properties.

In the process in accordance with our invention the silver-halide dispersion is prepared in normal gelatin in accordance with the usual procedure. The silver-halide formation and such ripening as is desired is carried out. There is then added to the silver-halide dispersion gelatin derivative in an amount which will give the mass the property of being acid coagulable. This may be a proportion of gelatin derivative of 2 to l derivative to gelatin, 4 to l, or, if desired, an even larger proportion of gelatin derivative may be added, although as a practical matter, proportions of less than to l are most satisfactory. The gelatin derivative is thoroughly stirred into the silver-halide dispersion whereupon acid is added to reduce the pH to less than 4.5, the amount of salt present determining the lower limit of the pH range. If the nitrate resulting as a by-product from the preparation of the silver halide is present, the pH may be reduced to 3 and coagulation will be obtained in this case, the salt being on the order of approximately 0.2 normal. If for some reason higher concentrations of salt are present, a still greater range of pH may be employed for the coagulation. Upon reducing the pH tothe coagulation range, the gelatin derivative coagulates and carries down the gelatin and silver halide therewith. The phenomenon which occurs is characterized by an enveloping of the silver-halide grains by the coagulated gelatin derivative so that a rainy mass is obtained. This mass may then be subjected to repeated washings, thereby removing substantially all of the water-soluble salts from the coagulum.

For some types of emulsions the coagulum may be employed directly without any further washing than the removal of the mother liquor from the precipitated material. For instance, in the preparation of emulsions for the coating of paper and other permeable materials, extended washing is not necessary. However, in the preparation of emulsion for coatin on film or glass, it is desirable to reduce the content of soluble salts below that which obtains in the coagulation after the mother liquor has been removed therefrom. This washin may be done by any one of several methods. The coagulum-may be rinsed by treatment with cool water, preferably with a pH adjusted to the isoelectric point of the gelatin derivative. The number of rinses necessary to reduce the salt content of the coagulum to the desired point is usually within the range of l to 4 changes of water. As an alternative method for washing the coagulum may be dissolved in water at an elevated pH, such as by using wat r taining a small proportion of sodium or ammonium hydroxide to bring the pH of the mass up to 6 or more. The temperature of the mass is raised to approximately 40 0., and the Whole is stirred for a few minutes to effect re-dispersion of the coagulum. After complete re-dispersion has been obtained, the gelatin derivative may be coagulated by the addition of an appropriate acid solution to reduce the pH to the coagulation point of the derivative. After the addition of the acid thecoagulum will settle and is separated from the mother liquor in the same manner as in the first coagulation step. The coagulation and re-dispersion operation may be repeated as often as necessary but for normal purposes one cycle of washing is suflicient.

, The coagulum which has been washed by either of the two general methods outlined above may then be re-dispersed to form photographic emulsions suitable for the subsequent finishing and coating operations by treating with the required quantity of water, normal gelatin or gelatin derivative and base to raise the pH of the Whole to 5 or 6 or even greater. The mixture of coagulum, water, gelatin or gelatin derivative and any other materials which have been added is then stirred at approximately 40 C. for the time required. to effect complete re-dispersal of the coagulum. The time required is normally of the order of ten to twenty minutes but may vary depending upon the chemical nature of the particular gelatin derivative used. The emulsion thus prepared behaves similarly to emulsions prepared using a similar emulsification and ripening technique in which noodle washing is employed. The emulsions prepared in accordance with our invention respond readily to the standard methods of chemical sensitization or after ripening, and optical sensitization. They may be coated by the techniques usual in coating photographic emulsions. The use of gelatin derivatives for obtaining washed emulsions presents considerable advantage over other techniques described in the literature for the washing of emulsions. It has been well known for years that gelatin silver-halide emulsions could be coagulated by the addition of suflicient quantities of suitable organic solvents of which methanol, ethanol, or acetone may serve as an example. Such procedures, however, have proved to be expensive and cumbersome because of the very large quantities of organic solvent which must be used per unit of emulsion since no chemical reaction between the gelatin and the solvent is in question. The gelatin coagulates and becomes insoluble in themedium through the well known effectof organic solvents to coagulate proteins.

In":th'e-v preparation of gelatin-silver halide emulsions accompaniedby the use of gelatin derivatives, the physical characteristics of water insolubility as related to pH are of vital importance. With gelatin derivativeswater insolubility is exhibited within the pH range ofapproximately 4 to 4.5. In the presence ofneutral electrolytes, however, the pH range-of water'insolubility isbroadened and may extend from 3to 4.5 or possibly evenmore. In the initial coagulation considerable neutral electrolyte is usually present in theform of potassium-nitrate (or other alkali metal salts) resulting from the double decomposition reaction between silver nitrate and potassium bromide, forinstance. In addition to this salt it is common practicethat some soluble halide also be present. Under such conditions the-adjustmentof pH in the-first coagulation is notparticularly critical. If, however, the coagulum is re-dispersed, asecond coagulation will take place at a much lower salt concentration and, thereforethe pH adjustmentnecessarywill be more critical. For this purpose we prefer to operate in the-range of 3.8 to 4.2

It is apparent that considerable advantage will accrue 'by the use of this method in that the concentration ofsilver halide in the final emulsionmay be adjusted to any desired'value without reference to the quantities of water, silver halide, and gelatin used in the initial emulsificat'ion reaction. Therefore, emulsions may be prepared with very small water content. An additional advantage of the coagulum method of operation lies in the considerable reduction of equipment necessary, since the washing operation-may be carried outin the usual emulsion- -making equipment, and the additional operations and equipment necessary for the usualwashing operation may beeliminated. We have found that the dicarboxylic acid-anhydride derivatives of .gelatin, such as of phthalic anhydridegare useful for preparing washed silver -halide dispersions and emulsions. These derivatives of gelatin and their:preparation are describedand claimed in Frame andYutzy application, Serial No. 768,474, filed of even date, now Patent No. ..2,525,753. We have found that the coagulation operation inaccordance with our inventionmay. -be carried out :either after the preparation of silver halide to remove water-soluble salts therefrom or. after a heat treatment thereof with appropriate chemical sensitizers so that the ucoagulated silver-halide grains maybe. obtained either beforeor after having been brought to deleterious effect on theirproperties when finally .made up in .theemulsion. We have foundthat -our invention-may .becarried out with any :of

the above-mentioned derivatives ofgelatinwithout regard as to the gelatin which has been. employed to form the derivative. Although wehave .found that the standard type of photographic r gelatin is very satisfactory in preparing emulsions in accordance with our invention, we havealso found-that other types of gelatin,-such tasithe tained at 50 C. whereupon it'was cooled to 40 C. One-half of this silver-halidedispersion'was roptimumphotographic speed. These grains may i .be dried at either stage in the cycle without solved in 900 cc.iof distilled water at '25"C.. In

another vessel g. of potassium bromide; 1 g. ofpotassiumdodide and:25 g. of gelatin were dissolved in900 cc. of distilled water. The temperatures of both solutionswere adjusted to 50 C. and the silver nitrate solution was added to the potassium bromide-gelatin solution, over a period of approximately ten minutes accompanied by vigorous stirring. During the ,addition of the silver nitrate solution and for ten minutes thereafter the. temperature was maintiivefhad been prepared by dissolving (g. of

gelatin in 1100 cc. of distilled water, adjusting thepH to 9.5 with20% sodium hydroxide and the temperature to '110" F. There was'added to this-solution 7 g. of benzene sulfonyl chloride over a period of ten minutes and the pH of 9.5

and the temperature of F. were maintained during this addition and for 45 minutes thereafter. Dilute sulfuric acid was then added to lower the pH to 6 and the resultant mass of gelatin derivative wasset, sliced, and dried;

After the gelatin derivative had been added to the silver-halide dispersion the dispersion was stirred for five minutes-at 40 C., after which approximately 20cc. of 5-N sulfuric acid were added to reduce the pH to 3.0. After standing at this pH for several minutes a coagulum of silver halide and gelatin settles out. The mother liquor was decanted 01f and the coagulum was redispersed in one liter of distilled water by stirring vigorously for five minutes at 40 C. There was then. added to the emulsion approximately 15 cc. of 3 N am- A 400 cc. portion of this emulsion was melted at 40 C. andB N ammonium hydroxide wasadded until the mixture was approximately neutral.

and theemulsion was subjected to a temperature of. 65 C. until optimum speed, contrast, and

reasonable fog were reached. For instance, the

emulsion was coated on 5 x '7 glass plates, was chilled and dried and tested sensitometrically ,by

exposure on .a photographic sensitometer and development in a photographic developer. Example 2.To the second portion of the silver-halid dispersion prepared as described .in

the first paragraphof Example 1 there was added 75 g. of the phenyl isocyanate derivative of gelatin, thereby imparting to the dispersion the .property of being acid coagulable.

The gelatin derivative used herewas preparedin the same mannerjas that of Example 1 except that phenylisocyanatewas employed instead of benzene sulfonyl chloride as the reagent. The coagulation, decantation, washing, and finishing of the emulsion followed the same procedure as .in Example 1. photographic proper A small amount of potassium bromide was added r according to the procedure well known in the art,

folldwd except that 50gxo'f aphthalic anhydride derivative of gelatinwas used insteadioflthe benzene sulfonylchloride-derivative. A dispersion was obtained which was acid coagulable.

The gelatin derivative used here was prepared by adding gi of phthalican-hydride in 100 .cc. *ofdry acetone over a 23-minute period to a solution of 100 g. of gelatin in 1000' cc. of water',.the mass being 'maintainedat 40 C. and at a pH of 955." After ten minutes the pH waslowered to? .0 with dilute sulfuric acid and the gelatin was "chill set, sliced, washed,'andl dried. The .coagulation, washing; and recoagulationi were carried but inthe'same manner as described-inthe;pre- =ceding examples. 9 The finished zemulsion' prepared as described in Examples 1 and 2 was coat- "ed' on glass plates and tested .sensitometrically. "This emulsion was found to have goodphoto- "graphicwproperties. T 1

Ezramp'le '4."The' same procedure was followed as" in Example 1 except that '75 g. of m-carboxy :ben'zene sulfonyl chloride derivative of gelatin I was mixed with "the silver-halide dispersion inste'ad'of the benzene sulfonyl chloride derivative.

--The' derivative employed was'prepared' by adding 10.5 g. of m-carboxy' benzene sulfonyl chloride in' 50 cc. of dry acetone to a solution of 100 810i gelatin in 900 cc. of water at 40 over aperiod "of two hours; The pH' of the gelatin solution was adjusted to 10.0 and maintained there by the use of 10% sodium hydroxide throughout the reaction. The pH was then adjusted to 7.0 with dilute sulfuric acid. The gelatin solution was se by chilling, sliced, washed and dried.

The emulsion obtained by the procedure described was washed by successive coagulations as described in Example 1, was brought to its final xvolume,land was finished and coated onto glass plates for sensitometrio tests. A photographic emulsion having good properties was obtained.

1 Example 5.The procedure described in Example 1 was followed except that in place of the benzene sulfonyl chloride derivative of gelatin 50g. ofp-tolylisocyanate derivative of gelatin was mixed with the silver-halide dispersion and after reduction of the pH to produce a 'coagulum, the mother liquor was decanted therefrom and the coagulum was redispersed in distilled water at 40 C. Recoagulation was obtained. byrai'sing 'the pH to 4.1 with 3 N ammonium hydroxide. The mother liquor wasdecanted off and after redispersing the coagulum in '75 g. of gelatin and sufficient water to adjust the weight to 1.36 kg. the emulsion was finished in the same manner as in Example 1. A portion of the finished emulsion was coated on glass plates and sensitometric tests showed that it had good'photographic properties.

Example 6.-The procedure of Example 1 was followed except thatthe derivative obtained by reacting maleic anhydride with gelatin was employed to impart acid coagulability to the silverhalide dispersion. The derivative employed was prepared by dissolving 50 g. of gelatin in 400 cc. of distilled water and adjusting the pH to 10 with sodium hydroxide. The mass was then,

heated to 120 F. and 12.5 g. of maleic anhydride was added over a period of approximately three tion. was added directly to the silver-halide dispersion.

, .Thez coagulation, .decantation, redlspersion} re- T v :paragraph'of Example 1. 60'

z coagulation with ammonium hydroxide and final .adjustment of the emulsion to its finishing vol- -ume"and composition were carried out inthe same manner as in Example 1. A portion of the finished emulsion was coated on glass plates and sensitometric tests showed that it had good photographic properties. i

coated on glass plates and upon testing sensitometrically was found to have good photographic Emample 8.The same procedure was followed chloride derivative of gelatin dissolved in 600 cc. of water was added to the emulsion in place of 'the benzene sulfonyl chloride derivative of gelatin to impart acid coagulability thereto. The method of preparing this derivative is described in- U. S. application No. 768,472 ofGordon F. Frame, filed of even date, now Patent No. 2,494,041 issued January 10, 1950. I'heparticular furoyl chloride derivative of gelatin used was prepared by reacting parts of gelatin in 1200 parts of water at a pH of 10 at 104 F. with 7.5 parts of furoyl chloride in 50 parts of dry acetone. The pH was machinedat. 10 during the addition of the furoyl chloride and'for fifteen minutes thereafter. The pH was then reduced to 6 .with dilute sulfuric acid, and the mass was chilled, noodled, washed two hours, melted, chilled, sliced, and dried. The preparation of the emulsion and the washing procedure described in Example '1 .werefollowed. After the emulsion was finished, it was coated onto glass plates, and sensitometric' tests showed good photographic properties.

Example 9.The procedurefollowed here was the same as that used in Example 7 except that v the coagulum-produced by acidifying the mixture of silver-halide dispersion and benzoyl chloride derivative of gelatin was washed twice in" cold water before final dispersion in the gelatin solution. The ammonia coagulation described in Examples '7 and'l was omitted. The final emulsion was finished by heat treatment and coated on I glass plates as described in Example 7. Sensitometric tests showed that the emulsion had satisfactory photographic properties.

7 Example 10.A silver-halide dispersion in gelatin was prepared as described in the first This dispersion was halved and to this half portion'was added 50 g. of abenzoyl chloride derivative of'gelatin as described in Example 7. To the resulting mixture 20: cc. of aqueous sulfuric acid was'added to reduce the pHtoB. A' coagulum of silver halide andgelatin formed and-was allowed to settle. The mother liquor was decanted from the coagulum, and the latter was redispersed in'one liter 'of distilled water at 40 C. and a pH of 6.5

. obtained by adding approximately 15 cc. of 3 N s ammonium hydroxide. The silver-halide dispersion was again coagulated by adding aqueous sulfuric acid to lower the pH of the mixture to 4.1,and'the mother liquor was again decanted therefrom. The coagulum was dedispersed in a solution containing 75 g. 1 of 1 gelatin and "sufficient 9 weight: of. water. tov bring th total weightto 1.36 After stirring fortwenty minutes at 40. C. the emulsion was finished by treating with heat and coating onto glass plates. The emulsion upon testing sensitometrically showed good photographic properties.

Example 11.-The procedure of the precedingexample was followed except that the. benzoyl chlorid derivative of gelatin was prepared from a glue stock instead of from high viscosity gelatin. The procedure of coagulating, washing, and decanting, final adjustment of composition, and finishing described in the examples above gave an emulsion having good sensitometric properties.

Example 12.-The procedure described in Example!) was followed except that the second half of the silver-halid dispersion prepared as described in Example 10 was employed with the exception that '75 'g. of the benzoyl chloride derivative of glue (or unrefined gelatin) was employed to impart acid. coagulating properties. to

the dispersion. The silver-halidedispersionwascoagulated, decanted and washed in cold water. The coagulum was then dispersed in 75 g. of gelatin solution as the vehicle therefor and ad.- justed to a total weight of 1.36 kg. This mixture was stirred for twentyminutes at 40 C. and1was then cooled to C. and chilled. A test portion of 400 cc. was melted at C. giving heat treatment for approximately forty minutes at C. and was coated on glass plates. The platecoatings were exposed and werefound to givegood sensitometric results.

Example 13.-The following solutions I were prepared: solution A, 200 cc: of aqueous solution containing 50 silver nitrate by weight; solution B, having a total volume of 200 cc. and containing 190 cc. of an aqueous solution containing 40% potassium bromide by weight and 9% cc. of a solution containing 25% potassium iodide by a weight, .65 g. of a polyvinyl.v alcohol solution containing 203% polyvinyl alcohol and 205 cc. of water stirred at 93 C. for fifteenminutes to assure complete solution of the. polyvinyl alcohol.

Then there was added 950 cc. of water,100-cc. of

28% ammonium hydroxide and 20 g. of urea. There was then added at a temperature of F. solutions A and B over a period of elevenminutes with good stirring. Solution B was added beginning fifteen seconds after beginning solution A. l

A small quantity of ethyl alcohol was added dropwise during this period to. reduce foam.

. After the dispersion hadbeen prepared cc. of.

g. of benzoyl chloride over a period of fifteen minutes with good stirring. The mass was maintained at a pH of 10 and a temperature of 40 C. for twenty-five minutes. I

The pH of the mixture of the silver-halide dispersion and the. gelatin derivative was re-- duced to 2 by the addition of aqueous sulfuric 1 0. adjusting the pH to. -7..5' with dilute sodium hy-1 droxide: and stirring .for twenty-five minutes: at

50C. The resulting emulsion was then cooled to 40?" the: pH was adjusted to .=61with dilute sulfuric acid and: coated on standard photoi graphic paper stock. Instead of polyvinyl alcohol or gelatin. other peptizing colloids may be employedin the preparation of the silver=halide dispersions in accordance with'our invention. 1

Weclaimr I l 1. In. a method of preparing washed silver halide dispersions; the stepswhich comprise mixing a water-soluble silver salt andxa water-solu ble halide saltin an aqueous. solution ofl-a peptizing colloid, mixing therewith atleast 2 parts of a gelatin derivativesper part. of the peptizing colloid, thereby rendering the silver halideadis-i persion coagulable at a pI-Iwithin the range of pH. 3,-4.5, which gelatin derivative is. selected from. the. group consisting of the aromatic sulfonyl chloride derivatives of gelatin, the carboxylic acid chloride derivatives of gelatin; the carboxylic acid anhydride derivativesof gelatin, the aromatic isocyanate derivatives of gelatin and the 1,4 diketone derivatives of gelatin, 'co

agulating the dispersion ofsilver halide by adlusting to said pH whereby. silver halide-peptizer-gelatin derivative grains areformedand subsequently separating those grains. fromthe liquidportion ofthe mass. 1 l p 1 2. In a method of preparing" washed silver halide dispersions,the steps which comprise mixing a water-solublesilversalt and a water-soluble halide salt in an aqueous. solutionofl gelatin as the peptizing colloid; mixing therewith at least 2 parts of a gelatin derivative per part of gelatin, thereby rendering the silver halide dispersion coagulable at a pH within the range of pH 3-4.5, which gelatinderivative is selected from the group consisting of. the aromatic sulinga water-solubleysilver salt and a water-solua ble halide salt in an aqueous solution of,poly-' vinyl alcohol as the: peptizing' colloid, mixing therewith at least 2parts of a gelatin derivative per partof. polyvinyl alcohol, thereby rendering the silver halide dispersion coagulable at apH within the r'angeof pH 3-4.5,;which gelatin derivative is selected. fromuthe group consisting of the. aromatic. sulfonylchloride derivatives 1 of gelatin, the carboxylic acid chloride derivatives of gelatin, the carboxylic acid anyhdride derivatives of. gelatin, the aromatic isocyanate derivatives of gelatin and the 1,4 diketone derivatives of gelatin, the carboxylic acid anhydride derivahalide by adjusting to said pH whereby silver halide-polyvinyl alcohol-gelatin derivative grains areformed and. subsequently separating those grains. from the liquid portion of the mass.

4. In a method of. preparing washed silver halide dispersionathe steps which comprise mixing. awater-soluble silver saltand a water-solua ble halide salt in an. aqueous solution of a peptizingj. colloid, mixing therewith at least 2' parts of 'an' aromatic "sulfonyl 'chlo'ride derivative er gelatin per part "of the peptizing colloid, thereby;

rendering the silver halide dispersion coagulable at a pH within the range of pH 3-4.5, coagulating the silver halide'dispersion-by adjusting to said pH whereby silver halide-peptizer -gel'atin derivative grains are formed and Subsequently separatingthe thus-formed grains from the liquid portion of the mass.

5. In a method of preparing washed silver halide dispersions, the steps which comprise mixing a water-soluble silver salt and a water-soluble halide salt in an aqueous solution of a peptizing colloid, mixing therewith at least 2 parts of a carboxylic acid anhydride derivative of gelatin per part of the peptizing colloid, thereby rendering the silver halide dispersion coagulable at a pH Within therange of pH 3-4.5, coagulating the silver halide dispersion by adjusting to said pH whereby silver halide-peptizer-gelatin derivative 'grains are formed and subsequently separating the thus-formedgrains from the liquid portion of the mass.

6. In a method of preparing washed silver halide dispersions, the steps which comprise mixing a water-soluble silver salt and a water-soluble halide salt in an aqueous solution of gelatin as the peptizing colloid, mixing therewith at least 2 parts of a carboxylic acid anhydride dcrivative of gelatin per part of the peptizing colloid, thereby rendering the silver halide dispersion'coagulable at a pH'within the range ofpI-I 3-4.5, coagulating the silver halide dispersion by adjustingto said pH whereby silver halidegelatin-gelatin derivative grains are'formed and subsequently separating the thus-formed grains from the liquid portion of the mass.

' 7. In a method of preparing Washed silver halide dispersions, the steps which comprise mixing together a water-soluble silver salt and awatersoluble'halide salt in an aqueous solution of a peptizing colloid, mixing therewith at" least 2 parts of th benzene sulfonyl chloride derivative of gelatin'per part 'of the peptizing colloid; thereby rendering the silver halide dispersion 'coagulable at a pH within the rangeo'f pH-3-'4;5; coagulating the silver halide dispersion by adjusting to said pH whereby silver'lialide-peptizergelatin derivative grains are formed and subsequently separating those grains from the liquid portion of the mass.

8. In a method-of preparing washed silverhalide dispersions'the steps which comprise mixing together a water-soluble silver salt "and a water-soluble halide salt in an aqueous solution of a p eptizing colloid, mixing therewith at least 2 parts of the phenyl i'socyanate derivative of gelatin per part of the peptizing 'colloidy-"thereby rendering the silverhalide'dispersion coagulable at a pH within the range of pH 3-4.5, coagulating the silver halide dispersion by adjusting to said pH whereby silver halide peptizer-gelatin derivative grains are "formed and; subsequently separating" those grains fromthe liquid portion of the mass.

'9. In a method of preparing washed silver hal ide dispersions, the steps which comprise'mix'ing together a water-soluble silver salt'and'a watersoluble halide'salt in an'aqueousfsolution of "a peptizing colloid, mixing therewith at least 2 parts of the phthalic anhydride derivative'ot gelatin per part of the peptizing colloid, thereby rendering the silver halide dispersion coagulable at a pH within the range of 'pH'3-4.5, coagulating the silver halide dispersion by-,adjustihgto said pH"wh'erebysilver halide peptizer-gelatin derivative grains are formed and subsequently separating those grains from the liquid portion ofthe mass.'

10. In a method of preparing washed silver halide dispersions, the steps which comprise mixin'g together a water-soluble silver salt and a water-soluble halide salt in an aqueous solution of 'a peptizing colloid, mixing therewith at least 2 parts of the benzoyl" chloride derivative of gelatin per part of the'peptiz'ing colloid, thereby rendering the silver-halide dispersion coagulable at a pH within the range of pH 3-4.5, coagulatmg the silver halide dispersion by adjusting to said pH 'whereby silver halide-peptizer-gelatin derivative grains "are formed and subsequently separatingthos'e' grains from the liquid portion of'the mass. Y1 v 11; In 'a method' of'preparing washed silver halide dispersionsibs steps which comprise mixing water-soluble silver salt and watersoluble-halidesaltin an aqueous solution of gelatin as the peptizing-colloid, mixing therewith at leas-t 2 parts of-the-phthalic anhydride derivative (if-gelatin per part ofthe peptizing' colloid, thereby rendering the silver halide dispersion coa'g'ulable at a pH within the range of pI-I- 3-4.5, coagulating thesilver'halide dispersion byadjusting to said pI-I whereby silver halide-peptizergelatin 'derivative grains are formed and subsequenuy separating those grains from the liquid portion of thelm'ass j 12. A method of preparing a washed'silver halide photosensitive emulsion which comprises mixinga water-soluble silver salt and a watersoluble halide salt in an" aqueous solution of a peptizing "colloid, mixing therewith 'at least 2 partsof the phthalic anhydride derivative of gelatin per part of the peptizing colloid, thereby renderingthe silver halide dispersion coagulable at a pH within the range of pH 3-4.5, coagulatingthe'silve'r halide dispersion by adjusting to said pH whereb'y silver halide-peptiZer-gelatin derivative grains are formed, separating those grains from the liquid portion of the mass and subsequent by mixing those grains with gelatin and water as a protective colloid for the silver halide whereby a photosensitive emulsion is formed, b q

13. In a method of preparing washed silver halide dispersions, the steps which comprise mixing a water-soluble silver salt and a watersoluble halide salt in an aqueous solution of a peptizing colloid, mixing therewith approximate- 1y 4 parts of a gelatin derivative per part of the pepti zing colloid, thereby rendering the silver halide'jdiSpersion coagulable at a pH within the range'of pI-I 3-4.5,which gelatin derivative is selected from the group consisting of the aromatic sulfonyl chloride derivatives of gelatin, the carboxylic acid chloride derivatives of gelatin, thecarboxylic acid anhydride derivatives of gelatin, the aromatic isocyanate derivatives of gelatin and the 1,4 diketone derivatives of gelatin, coagulating the dispersion of silver halide by adjusting to said pH whereby silver halidepeptizer-gelatin derivative grains are formed and subsequently separating those grains from the liquid portion of the mass.

HENRY C. YUTZY. I FREDERICK J. -RUSSELL.

(References on following page) 13 REFERENCES CITED Number The following references are of record in the 2489341 file of this patent:

UNITED STATES PATENTS 5 Number Number Name Date 479,419 1,844,716 Lambert Feb, 9, 1932 537,256 2,139,774 Sheppard et a1 Dec.13, 1938 580,504 2,282,001 Russell et a1 May 5, 1942 14 Name Date Waller Nov. 29, 1949 FOREIGN PATENTS Country Date Great Britain Feb. 4, 1938 Great Britain June 16, 1941 Great Britain Sept. 10, 1946 

1. IN A METHOD OF PREPARING WASHED SILVER HALIDE DISPERSIONS, THE STEPS WHICH COMPRISE MIXING A WATER-SOLUBLE SILVER SALT AND A WATER-SOLUBLE HALIDE SALT IN AN AQUEOUS SOLUTION OF A PEPTIZING COLLOID, MIXING THEREWITH AT LEAST 2 PARTS OF A GELATIN DERIVATIVE PER PART OF THE PEPTIZING COLLOID, THEREBY RENDERING THE SILVER HALIDE DISPERSION COAGULABLE AT A PH WITHIN THE RANGE OF PH 3-4.5, WHICH GELATIN DERIVATIVE IS SELECTED FROM THE GROUP CONSISTING OF THE AROMATIC SULFONYL CHLORIDE DERIVATIVES OF GELATIN, THE CARBOXYLIC ACID CHLORIDE DERIVATIVES OF GELATIN, THE CARBOXYLIC ACID ANHYDRIDE DERIVATIVES OF GELATIN THE AROMATIC ISOCYANATE DERIVATIVES OF GELATIN AND THE 1,4 DIKETONE DERIVATIVES OF GELATIN, COAGULATING THE DISPERSION OF SILVER HALIDE BY ADJUSTING TO SAID PH WHEREBY SILVER HALIDE-PEPTIZER-GELATIN DERIVATIVE GRAINS ARE FORMED AND SUBSEQUENTLY SEPARATING THOSE GRAINS FROM THE LIQUID PORTION OF THE MASS. 